Why does tea taste different when it’s cold?

Chris - Great question. I think there are probably three, possibly four reasons for this. The principle reason is the temperature. When you take food and drink into your mouth what we call taste is large down to smell. You can prove this yourself. If you take something strongly flavoured into your mouth and then hold your nose you'll notice that it appears to lose most of its taste. That's because when you put warm things or things that are cold into your mouth the heat in your mouth volatilises, in other words, turns into vapour some of the volatile chemicals in the food. They then drift up the back of your nose into your nasopharynx where they dock with chemical receptors in what's called your olfactory epithelium. That's where you smell. This tells the brain that particular flavours are present. Most of the food we eat we actually experience the taste as a smell. When you put cold tea into your mouth the temperature means that many of the volatile chemicals that are in the tea don't escape the tea in the same way or at the same rate that they would do with hot tea. The more energy that these chemicals are given the more of them will be driven off. This means that as a result less stimulation goes into the olfactory epithelium so the taste is less strong for some chemicals than others. The tea tastes different. The second point is that when tea's cold the viscosity is very different. It's a thicker fluid than when it's hotter. This means that the stimulation into your mouth and tongue is a bit different. So it tastes and feels different in the mouth which also changes your perception of the flavour of the tea. Then there's another possibility and that's when tea has stood for a long time and gets cold it has separated out according to density of the different components of the tea. If you have got a hot cup of tea you have thermal activity in the fluid so hot things are rising to the top and cold fluid is going to the bottom. This keeps the contents mixed. When you have a tea cup standing there for a long time and the temperature's fallen then it stops mixing like this and things get separated out. The fatty, less dense things go to the top and the more dense things go to the bottom. The mouthful of tea you get isn't a mixture of tea like it would have been before when it was hot.